Automatic speed control apparatus for controlling vehicle speed at set

Abstract

An automatic speed control apparatus for controlling the running speed of a vehicle at a constant set speed includes an auxiliary intake passage providing direct communication between portions of a main intake passage upstream and downstream from a throttle valve so as to bypass the throttle valve, an auxiliary intake air valve adapted for controlling the flow rate of air in the auxiliary intake passage, and a fuel supply cut-off means for suspending the supply of fuel to the engine from a moment at which a fuel supply cut-off condition is met, which requires the throttle valve to be set at the minimum opening position and the engine speed to be higher than a predetermined fuel supply cut-off engine speed, until the moment at which a predetermined fuel supply recovery condition is met. An actuator for actuating the throttle valve is controlled so as to vary the degree of opening degree of the throttle valve and enable the vehicle to run at the constant set speed. The auxiliary intake air valve is controlled in such a manner that the flow rate of air in the auxiliary intake passage is reduced before the fuel supply cut-off condition is met during motion of the vehicle under the control of the automatic driving apparatus. The rate of fuel supply to the engine has therefore been reduced before the fuel supply is actually cut-off so that the amount of change in the engine output torque and, hence, the level of shock produced by the change in the engine output torque are reduced when cut-off of the fuel supply is executed.